Island Overrun With Rats Completely Recovers in Only 11 Years After Ecosystem Had Been Decimated

Formerly known as ‘Rat Island’, this beautiful spot in the Aleutian islands has become a new example of how ecosystems can fully recover to their natural state in little more than a decade.

Along the western edge of the Alaskan archipelago, the land had inadvertently become populated with rodents, leading to the ignominious name Rat Islands. The non-native invaders were accidentally introduced to these islands following shipwrecks dating back to the 1700s and World War II occupation.

Known to be among the most damaging invasive animals, the resilient rodents adapted and thrived in the new setting, overwhelming the island ecosystems, disrupting the natural ecological order and driving out native species.

But a coordinated conservation effort removed the rats on the renamed Hawadax Island and a new study led by a University of California San Diego researcher has documented the remarkable recovery.

“We were surprised that the level of recovery unfolded so quickly—we thought it could be longer,” said Carolyn Kurle, an associate professor in the UC San Diego Division of Biological Sciences Section of Ecology, Behavior and Evolution and lead author of the study in published in Scientific Reports.

Kurle, along with researchers from UC Santa Cruz, conducted surveys on Hawadax in 2008 when the invasive rodents dominated the island ecosystem, finding that the rats unleashed a cascade of disruption for the island’s food chain.

Rats preyed upon shore bird eggs and chicks, nearly wiping out the island’s breeding shorebird population. Without birds consuming herbivorous seashore invertebrates such as snails and limpets, the island’s intertidal plant-eaters flourished, significantly driving down the abundance of the marine kelp.

To reverse these effects, a coordinated conservation strategy to save the native species on Hawadax removed the rats with poison in 2008, and presented a rare case in which researchers were able to compare the ecosystem after five years and, later found a fully recovered system after 11 years.

“Sometimes it’s hard to say that a conservation action had any sort of impact, but in this particular case we took a conservation action that was expensive and difficult, and we actually demonstrated that it worked,” wrote Kurle. “But we didn’t expect it to be so fast.”

After the rat eradication effort conducted by Island Conservation, the U.S. Fish and Wildlife Service, and The Nature Conservancy, the seabirds returned and are again consuming the seashore invertebrates, which has allowed the recovery and rebound of the kelp community.

“When the birds returned it led to an entirely different structure in the marine community on this island.”